Telescopes Buying Guide

Whether you're a budding astronomer  or a leisurely star gazer, the right telescope can mean the difference between seeing fuzzy balls of light and distinct planets  with rings.  But buyers shouldn't let their passions for the skies lead them to bad buying decisions--take the time to research your options before making any bold purchases.  Your wallet and the heavens will thank you.

Before Buying

• Consider your purpose.  If you're more of a casual observer, then you don't need to go for anything fancy.  Keep it simple and lightweight, with a particular focus on good field of view.  But if you or your child have an interest that you intend to cultivate beyond the hobby realm, you might want to opt for something a bit more expensive that's got some extra features to go along with good optic quality.
• Good telescopes range from around  £150-£390.  But just because it has extra features doesn't mean it's better--especially if it's too complex to operate on your own.
• Consider your place.  From where will you be observing the night sky?  The bright lights of city often obscure your view, and thus your aperture will need to be adjusted accordingly.

Dos and Don'ts

• Say no to department stores.  Aim for a company that specializes in astronomy-related tools and equipment  if you want to get something of long-lasting quality.
• Christmas isn't always merry.  During the holiday season, toy stores stock up on products that look like telescopes, but don't do much of anything.  They have poor mountings and eyepieces, and often claim to be able to magnify objects by impossible amounts.
• Magnification may be meaningless.  Don't buy a telescope based on its magnification claims.  The way to comparison shop is by looking at the aperture, or the size of the mirror.
• Mounts are critical.  Without a steady mount, you wont be able to focus your telescope properly.  Get a tripod that looks simple, yet sturdy.
• It's okay to accessorise.  High-quality eye pieces  and electric focusers  may cost you some extra cash, but they'll also enhance the viewing experience.

Choosing

Telescope Types
Refracting Telescope  Refraction is the bending of light as a result of its passage from one medium to another.  In a refracting telescope, a lens with curved surfaces allows light to pass from air to glass and then back to air, bending it toward the optical axis of the lens. If the surfaces of the lens are shaped properly, the light is brought to a focus so you can see the night sky clearly. Advantages They have a completely clear aperture. No central obstruction causes light to be scattered from brighter to darker areas, and thus they have better contrast.  They are low maintenance. Lenses do not require re-coating like mirrors do, and the optical tube assembly of a refractor doesn't ever require realignment because it is fixed into place. Disadvantages Because it  is a closed-tube assembly, it can require a longer amount of time to cool to ambient temperature. Some blurring and colour changes can occur when looking at particularly bright images. They carry a weighty price-tag.	Reflecting Telescope  A reflecting telescope contains two mirrors — a large primary mirror at the bottom of the tube and a small, flat secondary mirror near the top of the tube. As light enters the tube, it strikes the primary mirror, is then reflected to the secondary mirror, and then reflected again into the eyepiece. Advantages They're cheap.  Because mirrors have only one optical surface--as opposed to apochromatic lenses which have between four and eight--they are much less expensive to produce. Disadvantages The secondary mirror can create a central obstruction that can cause some scattering of light and loss of contrast. They can create comas--stars at the edge of the field of view look like comets. Mirrors require recoating after several years. They are fragile.	Catadioptric Telescope  These scopes also are known as compound telescopes and are hybrids that incorporate both refractor and reflector elements in their design.  They commonly have a spherical primary mirror in the back and a glass corrector plate in the front. This telescope is used primarily for photography. Advantages They have a very long focal length in a very short, portable package. They can use a lighter mount. Disadvantages They are also subject to a central obstruction.

Related Guides

Optics	Binoculars	Science Toys	Night Vision Devices

External Links

• Astronomy.com:  Historical descriptions of the different types of scopes. 
• FindAScope.com:  Advice for buying your first telescope.
• Space.com:  Answers to all your astronomy FAQs.
• ScopeTronics.com:  A list of advantages and disadvantages for each type of scope.